In the process of development toward broadband and mobile networks, the 3rd Generation Partnership Project (3rd Generation Partnership Program, 3GPP) has proposed a long term evolution (Long Term Evolution, LTE) solution for a mobile access network, namely, an evolved universal mobile telecommunications system (UMTS) terrestrial radio access network (Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, E-UTRAN), and a system architecture evolution (System Architecture Evolution, SAE) solution for a mobile core network, namely, an evolved packet core network (Evolved Packet Core, EPC). The E-UTRAN and EPC constitute an evolved packet system (Evolved Packet System, EPS). A user equipment (User Equipment, UE) may access the EPC through the E-UTRAN, and may also access the EPC through a universal mobile telecommunications system terrestrial radio access network (Universal Mobile Telecommunication System Territorial Radio Access Network, UTRAN) or a global system for mobile communications (Global System for Mobile Communications, GSM)/enhanced data rate for GSM evolution (Enhanced Data rate for GSM Evolution, EDGE) radio access network (GSM EDGE Radio Access Network, GERAN).
Idle mode signaling reduction (Idle mode Signaling Reduction, ISR) is a mechanism provided for reducing signaling interaction when a UE in an idle mode reselects a radio access network. ISR may include two states: an activated state and a deactivated state. For example, the UE performs reselection between the E-UTRAN and the UTRAN/GERAN. In an ISR activated scenario, the UE needs to register with a mobility management entity (Mobility Management Entity, MME) in the E-UTRAN and a serving general packet radio service (General Packet Radio Service, GPRS) support node (Serving GPRS Supporting Node, SGSN) in the UTRAN/GERAN simultaneously. In the ISR activated scenario, a serving gateway (Serving GateWay, S-GW) maintains connection information of the MME and connection information of the SGSN simultaneously. The MME and SGSN store connection information of each other, that is, the MME stores connection information of the SGSN, and the SGSN stores connection information of the MME. Storing, by the S-GW, connection information of the MME and connection information of the SGSN simultaneously means ISR activation for the S-GW; storing, by the MME and SGSN, connection information of each other means ISR activation for the MME and SGSN.
In the ISR activated scenario, when the S-GW receives downlink user plane or control plane data of the UE, the S-GW triggers, according to the stored connection information of the MME and connection information of the SGSN, the corresponding MME and SGSN to page the UE. Therefore, no matter whether the UE currently camps in the E-UTRAN or UTRAN/GERAN, the UE can respond to a paging message of the network (that is, a mobile terminating service of the UE is available).
However, in the ISR activated scenario, in the case of an MME failure, for example, MME restart (Restart, which may also be referred to as reset, Reset) and non-restart, the SGSN and S-GW can detect the MME failure, and then execute an ISR deactivation operation respectively, that is, delete the stored connection information of the MME respectively. In this case, when the S-GW receives the downlink user plane or control plane data of the UE, because the S-GW has deactivated ISR, only the SGSN is triggered to page the UE. If the UE camps in the E-UTRAN at this time, the UE cannot receive the paging message sent by the SGSN, resulting in interruption of the mobile terminating service (that is, the mobile terminating service is unreachable), and thereby reducing reliability of the mobile terminating service. A same problem also exists when the SGSN restarts.